Filter of processing volume ratio adapted screw press type

ABSTRACT

A screw press type filter which comprises an alternately superposed arrangement of annular fixed plates ( 10 ) and annular movable plates ( 11 ), a filter cylinder ( 2 ) defining a fixed cylindrical space ( 12 ) by a row of openings of the fixed plates with both end portions of a screw ( 5 ) passed through this cylindrical space extending to inlet and outlet chambers ( 1, 3 ), and mechanisms ( 15, 16 ) for turning the movable plates in accordance with the rotation of the screw also provided, wherein the volumes of the spaces between adjacent ridges of the screws in the filter cylinder are reduced gradually from an inlet toward an outlet so that such a volume decrease corresponds to a gradual decrease in the water content of an object material being processed.

TECHNICAL FIELD

The present invention relates to a screw press type filter for filteringraw water containing sludge and other suspensions to separate it intofiltrate and dehydrated cake.

BACKGROUND ART

As for conventional screw press type filters, there is, for example, athrough-screw type filter cylinder system, as disclosed in JapanesePatent Publication No. SHO 63-65364 (U.S. Pat. No. 1,520,106). A filterof this system comprises a drum, a filter cylinder installed in asubstantial length excluding the opposite ends of the drum for filteringraw water to separately migrate the water content thereof radially frominside to outside of the drum, a number of through-holes formed in theperipheral surface of the drum in said substantial length, a screwinstalled throughout the length of the drum to extend through saidfilter cylinder, the spaces within said drum at the opposite endsthereof being used as an inlet chamber for raw water and an outletchamber for dehydrated cake. The filtration passage in the filtercylinder is defined by small clearances between alternating annularfixed and movable plates that constitute said cylinder.

In the above arrangement, normally as the water content is pressed outfrom the clearances between the plates toward the outer periphery of thefilter cylinder, the volume of an object material to be processed (theresidue remaining after the pressing of the raw water) that is pressedagainst the screw vanes corresponding to one pitch is progressivelyreduced according to the amount of water pressed out. In contrastthereto, in the usual construction wherein the volume ratio (processingvolume/unit length) and the screw pitch are constant throughout thelength of the filter cylinder, the screw load becomes lighter as therear end of the filter cylinder is approached, resulting in the rear endof the screw feeding no substantial load.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a screw press whereinthe processing capacity per screw pitch of the filter cylinder(volume/screw pitch) is progressively reduced over a region ranging fromthe inlet to the outlet, according to the amount of an object materialprocessed per pitch of the screw normally decreasing, as the objectmaterial is pushed to move in a filter cylinder to press out its watercontent.

To achieve the above object, the invention provides a screw press typefilter comprising:

a) a filter cylinder including an alternately superposed arrangement ofa number of annular fixed plates each having an inner diameter, and anumber of annular movable plates each having an inner diameter slightlylarger than the inner diameter of said fixed plates and capable ofshaking in the same plane with an amplitude corresponding to adifference between the respective inner diameters of said fixed andmovable plates, with small filtration clearances defined therebetween,said filter cylinder having a fixed cylindrical space defined by theseries of openings in said fixed plates; and

b) a screw installed in the cylindrical space of said filter cylinder toextend therethrough, with a mechanism provided for shaking said movableplates by rotation of the screw, whereby raw water fed in through aninlet port in an inlet end of said filter cylinder is pushed orpropelled toward an outlet port in an outlet end thereof while saidfiltration clearances between the plates are always reproduced by theshaking movement of the movable plates;

c) said screw press type filter being characterized in that processingvolume per screw pitch of said filter cylinder is progressively reducedover a region ranging from the inlet end to the outlet end.

In the above arrangement, there are three systems of means forprogressively reducing the processing volume per screw pitch over aregion ranging from the inlet end to the outlet end: {circle around (1)}means for progressively reducing the pitch of the screw over a regionranging from the inlet end to the outlet end of said filter cylinder,{circle around (2)} means for progressively increasing the shaftdiameter of the screw over a region ranging from the inlet end to theoutlet end of said filter cylinder, and {circle around (2)} means forprogressively reducing the inner diameter of the filter cylinder and theprojected area of the cross section of the screw corresponding theretoover a region ranging from the inlet end to the outlet end of saidfilter cylinder.

In a screw press filter according to the invention in which theprocessing volume per screw pitch of the filter cylinder isprogressively reduced over a region ranging from the inlet end to theoutlet end according to one of said three systems, the processing amountper screw pitch of an object material which is subjected to gradualwater press-out to become harder is gradually accordingly reduced,whereby the distribution of the load on the screw is made uniform toensure efficient water press-out throughout the length of the filtercylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

A screw press type filter of a preferred embodiment according to theinvention will be described with reference to the drawings, in which:

FIG. 1 is a longitudinal sectional view showing an embodiment of a presstype filter of the type in which the screw pitch is progressivelyreduced;

FIG. 2 is a sectional view taken in the direction of arrows I—I in FIG.1;

FIG. 3 is a fragmentary sectional view taken in the direction of arrowsII—II in FIG. 2;

FIG. 4 is a longitudinal sectional view showing an embodiment of a screwpress type filter of the system in which the screw shaft diameter isprogressively increased; and

FIG. 5 is a longitudinal sectional view showing an embodiment of a screwpress type filter of the system in which the inner diameter of thefilter cylinder is progressively reduced.

BEST MODE FOR EMBODYING THE INVENTION

A screw press type filter of a first embodiment according to theinvention, as shown in FIG. 1, comprises an inlet chamber 1, a filtercylinder 2 and an outlet chamber 3 that are connected in series, as seenfrom the righthand in FIG. 1, wherein a screw 5 extending throughout thelength of the filter from the inlet chamber 1 to the outlet chamber 3passes through the cylindrical space 4 in the filter cylinder 2. Aninlet port la is formed in the upper portion of the inlet chamber 1 forreceiving raw water to be processed, while an outlet port 3 a is formedin the lower portion of the outlet chamber 3. The screw 5 is shaped suchthat the pitch is continuously reduced from the pitch A of those screwvanes which are at the inlet to the pitch B (accordingly, B<A) of thosescrew vanes which are at the outlet, so as to be adaptable to the volumeof the object material which is dehydrated to gradually decrease involume.

The front and rear end plates 6 a and 6 b, respectively of the filtercylinder 2 define the boundaries of the inlet and outlet chambers 1 and3. A rear end cylinder 7 forming an extension of the inner wall of thefilter cylinder projects through the aligned opening in the rear endplate 6 b. The diameter-reduced rear end shaft portion 5 b of the screwshaft 5 a has fitted thereon a valve disk 8 for controlling thedischarge of the processed material. The valve disk 8 is supported atthe back by a spring 9 installed on the rear end shaft portion 5 bbehind the valve disk, said spring 9 urging the valve disk 8 against theend edge of the rear end cylinder 7 and against the rear end of thescrew shaft 5 a (the root of the shaft portion 5 b), so that the outletof the filter cylinder 2 is closed during the downtime of the device anduntil the processed material is fed in under pressure after the start ofthe operation of the apparatus.

The filter cylinder 2 comprises a number of annular fixed plates 11fixed in position by four support bars 10 (FIG. 2) or the like carriedbetween the front and rear end plates 6 a and 6 b, and a number ofannular movable plates 12 having a center opening diameter slightlylarger than that of the annular fixed plates, the annular fixed andmovable plates alternating with each other with slight filtrationclearances defined therebetween. The movable plates 12 can be shaken inthe same plane with an amplitude corresponding to the difference in borediameter between the movable and fixed plates by a cam mechanism to belater described. In this case, the series of openings in all fixedplates 11 defines said cylindrical space 4, and there is no possibilityof the movable plates 12 narrowing the inner Peripheral surface of thecylindrical space 4 due to their shaking movement. Therefore, the outeredge of the vanes of the screw 5 can snugly engage this inner peripheralsurface and continuously rotate.

The front end of the screw shaft 5 a and the rear end shaft portion 5 bare respectively supported by bearings installed on the outer end plates13 a and 13 b of the inlet and outlet chambers 1 and 3, and the rear endof the shaft portion 5 b projecting out of the bearing mounted on theouter end plate 13 of the outlet chamber is driven for rotation throughgears, or the like, and is operatively connected to another rotary shaft15 by a gear train 14. As is clear from FIG. 2, the rotary shaft 15extends below the filter and between the outer end plates 13 a and 13 band is reduced in diameter along its portion located in the filtercylinder 2 and the diameter-reduced portion 15′ has an axially extendingcam key 16 on its peripheral surface of said diameter-reduced portion15.

The fixed plates 11 are perfectly annular plates having outerperipheries defining the outer peripheral surface of the filter cylinder2 and openings defining the aforesaid cylindrical space 4 and aresupported by said four support bars 10 extending therethrough and arespaced from each other by spacers 17 in the form of small circularplates also supported by said support bars 10 extending therethrough. Onthe other hand, movable plates 12 are annular plates having an outerperiphery which is somewhat smaller than that of the fixed plate 11 andwhich is formed with recesses 18 surrounding the spacers 17 with asufficient margin left therearound, and an opening 19 somewhat larger indiameter than the opening in the fixed plate 11 (i.e., than thecylindrical space 4), with upper and lower holes 20 a and 20 b formed inthe upper and lower regions of the movable plates 12, the upper holes 20a having a fulcrum bar 21 loosely fitted therein, the lower holes 20 bhaving fitted therein the intermediate narrow diameter portion 15′ ofthe aforesaid rotary shaft 15. The lower holes in the fixed plates 11through which the narrow diameter portion 15′ extends, as clearly seenfrom FIG. 1, have a diameter which corresponds to, or is greater than,the circular path of the cam key 16, whereby the fixed plates 11, intheir fixed state, allow the rotation of the narrow diameter portion 15′and hence the rotary shaft 15. Further, since the aforesaid lower holes20 b in the movable plates 12 have a diameter which is slightly largerthan the diameter of the narrow diameter portion 15′ plus the height ofthe projection of the cam key 16, the movable plates 12 are cam-drivento perform an eccentric rotation as the cam key 16 is rotated, so thatthe movable plates 12 are shaken mainly vertically around the fulcrumbar 21 extending through the upper holes 20 a.

Next, as is clear from FIG. 3, which is an enlarged fragmentary sectiontaken in the direction of arrows II—II in FIG. 2, the spacers 17 in therecesses 18 have a thickness which determines the spacing betweenadjacent fixed plates 10, which, in this case, is a thickness slightlylarger than the thickness of the movable plates 11, with the result thata small filtration clearance is defined between adjacent plates 11 and12; thus, the filter cylinder 2 (FIG. 1) composed of an arrangement oflarge numbers of plates 10 and 11 is completed.

In the construction of the first embodiment described above, when thescrew 5 is driven, the rotary shaft 15 is simultaneously rotated by thegear train 14 and the rotation of the cam key 16 causes the lower holes20 b (see FIG. 2) in the movable plates 12 to perform an eccentricrotation, and attending the partial eccentric rotation, as describedabove, all the movable plates 12 shake within the range allowed by thefloat movement of the upper holes 20 a around the fulcrum bar 21. Inthis case, the height of the cam key 16 is set to be equal to thedifference in inner diameter between the fixed and movable plates 11 and12, and the difference between the inner diameter of the small holes 20a and the diameter of the fulcrum bar 21 is set to be approximatelyequal thereto. Therefore, the openings 19 in the movable plates 12 aredimensioned such that in the lowermost position shown in FIG. 2, theirupper edges coincide with the upper edge portions of openings in thefixed plates 11, i.e., the upper end of the inner peripheral surface ofthe filter cylinder 2, while in the uppermost position when the rotaryshaft 15 has rotated by half a revolution, their lower edges coincidewith the lower edge portions of the openings in the fixed plates 11,i.e., the lower end of the inner peripheral surface of the filtercylinder 2; thus, the movable plates 12 never get into the inside of thefilter cylinder inner peripheral surface 22 during one revolution of therotary shaft 15.

The raw water fed in through the inlet port la is propelled by the screw5 in the inlet chamber 1 from which it is fed to the filter cylinder 2.The raw water gradually pressed by the screw 5 within the filtercylinder 2 is filtered radially through the filtration clearances, whichare always (slidingly) reproduced between the movable and fixed plates12 and 11 by the shaking of the movable plates 12, the filtrate beingdischarged through the outer periphery. The decrease of the watercontent of the object material, that is, the volume-decreasing of theobject material is initially made as the compression and dehydrationproceed when the object material is being advanced by the screw 5. Inthis embodiment, the pitch of the screw 5 is correspondingly reducedover a region ranging from the inlet chamber 1 to the outlet chamber 3.Therefore, it is possible to eliminate the drawback of the conventionalapparatus that the intensity of the load of the object material on thescrew 5 greatly decreases from the optimum value with advancing positionso that the object material, insufficiently processed above a certainlevel, reaches the outlet chamber 3 and is discharged through the outletport 3 a.

Thus, in the screw press type filter in this embodiment, the amount ofthe raw water (the object material) corresponding to one pitch ispropelled by the screw 5 having a gradually decreasing pitch, so thatthe volume to be processed/unit time (the processing rate) slows down asthe object material moves to a downstream region. Therefore, the objectmaterial, whose sludge concentration is now increased and whosedehydration rate:pressure relationship is now lowered, can be processedfor a longer period of time for further dehydration, with the resultthat the water content of the cake discharged through the outlet port 3a can be fully reduced.

FIG. 4 shows an embodiment of a filter of the type in which the screwshaft diameter is progressively increased, which is a second form of theinvention. In this embodiment, there is no change in the screw pitch asin the filter shown in FIGS. 1 and 2, and instead the diameter of theshaft 5 a′ of the screw 5′ is progressively increased over a regionranging from the inlet chamber 1 to the outlet chamber 3, for example,from the diameter A′ immediately before the filter cylinder 2 to thediameter B′ located short of the outlet chamber in the filter cylinder 2(B′>A′). The rest of the arrangement is the same as in the embodimentshown in FIGS. 1 and 2, and like parts are marked with like referencenumerals to omit a description thereof.

In this embodiment, the diameter of the screw shaft 5 a′ is increasedcorrespondingly to a decrease in the water content of the objectmaterial, i.e., the volume of the object material in the screw pitch,which decreases over a region ranging from the inlet chamber 1 to theoutlet chamber 3, whereby the volumes of the spaces between adjacentridges of the screw are reduced. Therefore, it is possible to eliminatethe drawback of the conventional device that the intensity of the loadof the object material on the screw 5′ greatly decreases from theoptimum value with advancing position so that the object material,insufficiently processed, reaches the outlet chamber 3 and is dischargedthrough the outlet port 3 a. That is, also in the screw press typefilter in this embodiment, the amount of the raw water (the objectmaterial) corresponding to one pitch is propelled by the screw 5′ to begradually brought to a position where the pitch space volume is reduced,thereby making it possible to effect further dehydration while retainingthe optimum intensity of the load on the screw 5′. As a result, thewater content of the cake discharged through the outlet port 3 a can besufficiently lowered.

FIG. 5 shows an embodiment of a filter of the type in which the innerdiameter of the filter cylinder is progressively reduced, which is athird form of the invention. In this embodiment, rather than making achange in the screw pitch or screw shaft diameter as in the precedingembodiment, the inner diameter of the filter cylinder 2′ isprogressively reduced over a region ranging from the inlet chamber 1 tothe outlet chamber 3, for example, from the diameter A″ immediatelybefore the filter cylinder 2 to the diameter B″ located short of theoutlet chamber of the filter cylinder 2 (B″<A″). Therefore, the vanediameter (projected diameter of the cross-section) of the screw 5″ iscorrespondingly progressively reduced. The rest of the arrangement isthe same as in the preceding embodiments, and like parts are marked withlike reference numerals to omit a description thereof.

In this embodiment, the inner diameter of the filter cylinder 2′ isreduced correspondingly to a decrease in the water content of the objectmaterial, i.e., the volume of the object material in the screw pitch,which decreases over a region ranging from the inlet chamber 1 to theoutlet chamber 3, whereby the volumes of the spaces between adjacentridges of the screw are reduced. Therefore, it is possible to eliminatethe drawback of the usual type that the intensity of the load of theobject material on the screw 5″ greatly decreases from the optimum valuewith advancing position so that the object material, insufficientlyprocessed, reaches the outlet chamber 3 and is discharged through theoutlet port 3 a. That is, also in the screw press type filter in thisembodiment, the raw water (the object material) corresponding to onepitch is propelled by the screw 5″ to be gradually brought to a positionwhere the pitch space volume is reduced, thereby making it possible toeffect further dehydration while retaining the optimum intensity of theload on the screws 5′. As a result, the water content of the cakedischarged through the outlet port 3 a can be sufficiently lowered.

INDUSTRIAL APPLICABILITY

As has been described so far, the present invention provides a screwpress type filter in which the processing volume in the space defined bythe screw pitch of the filter cylinder is gradually reduced, therebymaking it possible to increase the filtration and dehydration functionand keep the water content of the processed cake sufficiently low.

What is claimed is:
 1. A screw press type filter comprising: a filtercylinder including an arrangement of alternatively spaced, parallelydisposed annular fixed and movable plates each having an inner diameter,the inner diameter of said movable plates being slightly greater thanthe inner diameter of said fixed plates, and said fixed and movableplates having small filtration clearances defined therebetween, andwherein said filter cylinder has a substantially constant cylindricalspace defined by openings in said fixed plates; an inlet port at aninlet end of said filter cylinder and an outlet port at an outlet endthereof; a screw installed in, and extending through, the cylindricalspace in said filter cylinder; means for rotating said screw identifiedby a rotary drive mechanism and cam means for moving said movable plateseccentrically with respect to said fixed plates; whereby raw water fedthrough the inlet port of said filter cylinder is pushed toward theoutlet port thereof while said filtration clearances between the platesare always reproduced by the shaking movement of the movable plates; avalve disk opposed to a rear end of said screw installed in a rear endof said filter cylinder, which contains the outlet port thereof, forclosing said outlet port until raw water to be processed is fed underpressure to said outlet port; and means for progressively reducing thepitch of the screw over a region ranging from the inlet end to theoutlet end of said filter cylinder.
 2. A screw press type filter as setforth in claim 1, characterized in that a shaft diameter of the screw isprogressively increased over a region ranging from the end of saidfilter cylinder containing said inlet port to the end of said filtercylinder containing said outlet port, thereby progressively reducing theprocessing volume.
 3. A screw press type filter as set forth in claim 1,characterized in that an inner diameter of the filter cylinder and anaxially projective diameter of the cross section of the screwcorresponding thereto are progressively reduced over a region rangingfrom the end of the filter containing the inlet port to the end thereofcontaining the outlet port, thereby progressively reducing theprocessing volume.